The form builder won't let me drag the field anywhere else in the form

Having issues in form builder (on existing forms). When I try to drag in new fields it just adds the field at the bottom of the form and subsiquently won't let me drag it anywhere else on the form. If I try and add any more fields it then only allows me to edit the last field I added.

Any ideas?

I cannot replicate this problem within your form. Here's a screenshot:

As you could see, I was able to drag the "Click to edit" field in the form. I think this is an issue that is isolated to your form and only happening to your browser. Please try editing the form in incognito/private mode and see if the issue persists. If not, I'd suggest clearing your browsing data, including your caches and cookies.